Replication selective oncolytic viruses have shown great promise as anti-tumor agents for solid tumors. These viruses are able to preferentially replicate within tumor cells, while being restricted in their ability to replicate in normal cells. The principle anti-tumor mechanism of oncolytic viruses is through a direct cytopathic effect as they propagate and spread from initially infected tumor cells to surrounding tumor cells, achieving a larger volume of distribution and anticancer effects. Herpes simplex virus (HSV) has been modified for oncolytic purposes, most commonly by deleting viral genes necessary for efficient replication in normal (non-dividing) cells but not tumor cells. The modifications include deletion of either the viral γ34.5 gene or ICP6 gene. The viral γ34.5 gene functions as a neurovirulence factor during HSV infection (Chou, et al, (1990) Science 250:1262-1266). Deletion of this gene blocks viral replication in non-dividing cells (McKie, et al., (1996) Br J Cancer 74(5): 745-52). The viral ICP6 gene encodes the large subunit of ribonucleotide reductase, which generates sufficient dNTP pools for efficient viral DNA replication and is abundantly expressed in tumor cells but not in non-dividing cells. Consequently, viruses with a mutation in this gene can preferentially replicate in—and kill—tumor cells. The oncolytic HSV G207, which has been extensively tested in animal studies and is currently in clinical trials, harbors deletions in both copies of the γ34.5 locus and an insertional mutation in the ICP6 gene by the E. coli lacZ gene (Walker, et al., (1999) Human Gene Ther. 10(13):2237-2243). Alternatively, an oncolytic type-1 HSV can be constructed by using a tumor-specific promoter to drive γ34.5 or other genes essential for HSV replication (Chung, et al., (1999) J Virol 73(9): 7556-64).
Oncolytic herpes simplex viruses (HSV) were initially designed and constructed for the treatment of brain tumors (Andreansky, et al., (1996) Proc Natl Acad. Sci. 93(21): 11313-11318). Subsequently, they have been found to be effective in a variety of other human solid tumors, including breast (Toda, et al., (1998) Human Gene Ther. 9(15):2177-2185), prostate (Walker, et al., (1999) Human Gene Ther. 10(13):2237-2243) lung (Toyoizumi, et al., (1999) Human Gene Ther. 10(18):3013-3029), ovarian (Coukos, et al., (1999) Clin. Cancer Res. 5(6):1523-1527), colon and liver cancers (Pawlik, et al., (2000) Cancer Res. 61(11):2790-2795). The safety of oncolytic HSVs has also been extensively tested in mice (Sundaresan, et al., (2000) J. Virol. 74(8):3832-3841) and primates (Aotus), which are extremely sensitive to HSV infection (Todo, et al., (2000) Cancer Gene Ther. 7(6):939-946). These studies have confirmed that oncolytic HSVs are extremely safe for in vivo administration.
Oncolytic HSVs have been exclusively constructed from HSV-1. HSV-2 has not been explored for the purpose of constructing oncolytic viruses. Nonetheless, HSV-2 has some unique features that enhance its potential as an oncolytic agent. For example, it has been reported that, unlike HSV-1, HSV-2 encodes a secreted form of glycoprotein G (gG) that affects the function of neutrophils, monocyte and NK cells (Bellner, et al. (2005) J Immunol 174(4): 2235-41). Such a property may provide an oncolytic virus derived from HSV-2 with the ability to resist the inhibitory effect of the body's innate immunity. Innate immunity is a quick response of the host to invading microorganisms and it has been found to be the major factor that restricts HSV replication in vivo (Dalloul, et al., (2004) J Clin Virol 30(4): 329-36; Wakimoto, et al., (2003) Gene Ther 10(11):983-90. Thus, an oncolytic virus derived from HSV-2 should replicate and spread even when the patient's body develops anti-HSV innate immunity.
Despite encouraging preclinical studies, results from early clinical trials have suggested that the current versions of oncolytic viruses, although safe, may only have limited anti-tumor activity on their own (Nemunaitis, et al., (2001) J. Clin Oncol. 19(2):289-298). Studies from the inventors' work have demonstrated that incorporation of cell-membrane fusion activity into an oncolytic HSV can dramatically improve the anti-tumor potency of the virus (Fu, et al., (2002) Mol. Ther. 7(6): 748-754; Fu, et al., (2003) Cancer Res. 62: 2306-2312. Such fusogenic oncolytic viruses produce syncytial formation in the tumor, directly enhancing the destructive power of the virus and promoting its intra-tumor spread (Fu, et al., (2003) Cancer Res. 62: 2306-2312). The uniquely combined tumor-destruction mechanism of syncytial formation and direct cytolysis by the fusogenic oncolytic HSV also facilitates in situ tumor antigen presentation, leading to potent anti-tumor immune responses (Nakamori, et al., (2004) Mol. Ther. 9(5): 658-665). Furthermore, the spread of a fusogenic oncolytic HSV through syncytial formation will allow it to maintain its anti-tumor activity even in the presence of neutralizing anti-viral antibodies in the host. Viruses can only replicate inside living cells and their replication usually requires activation of certain cellular signaling pathways. Many viruses have acquired various strategies during their evolution to activate these signaling pathways to benefit their replication. The large subunit of herpes simplex virus type 2 (HSV-2) ribonucleotide reductase (ICP10 or RR1) contains a unique amino-terminal domain which has serine/threonine protein kinase (PK) activity. This PK activity has been found to activate the cellular Ras/MEK/MAPK pathway (Smith, et al., (2000) J Virol 74(22): 10417-29).
Luo and Aurelian describe various vectors comprising different deletions of the ICP10 gene in HSV-2 to demonstrate the relationship between particular motifs and certain activities (Luo and Aurelian, (1992) J Biol Chem 267(14): 9645-53). Modified and deletion constructs of the HSV-2 ICP10 gene have been used to demonstrate particular characteristics of the ribonucleotide reductase domain (Peng et al. (1996) Virology 216(1): 184-96).
Deletion of the PK domain (ICP10 PK) from the ribonucleotide reductase gene severely compromises the ability of the virus to replicate in cells where there is no preexisting activated Ras signaling pathway (Smith et al (1998) J. Virol. 72(11):9131-9141).
U.S. Pat. No. 6,013,265 is directed to a vaccine that provides protection from challenge by HSV-2, wherein the protein kinase domain of ICP10 has been deleted, which leads to deleterious effects on the ability of HSV-2 to infect and transform cells.
The present invention fulfills a need in the art by providing novel therapeutics for the treatment of cancer utilizing a modified HSV-2.